Cory Parish would have been happy with any ride for the powerful Lindsay Park operation, let alone in a Caulfield Cup.

Now he has scored his first Group One win by guiding Boom Time to an upset victory in the $3 million race.

Parish had been scheduled to ride in Sydney on Saturday before Boom Time's owner and co-trainer David Hayes made the last-minute decision to enter Boom Time in the Cup.

Hayes, who heads the Lindsay Park organisation, operates with his son Ben and nephew Tom Dabernig.

"Tom came back to me and said 'oh, a change of plans, would you like to ride Boom Time in the Caulfield Cup'," Parish said.

"I said of course, I'm definitely free for that."

Parish usually spends five days a week riding for the Lindsay Park team, although he often misses out on the top Saturday races.

"I put in the work and I just get what I can," he said.

"If they put me on something, I'm on it. If they put someone else, I don't complain.

"I just go with the flow, get what I can and try and get the best I can."

Giving the Caulfield Cup ride to Parish was an easy decision for David Hayes who also sent him to Sydney three weeks ago to ride third-placed Snitzson in the Epsom Handicap.

"He knew the horse. He knew he went a bit fast last week (in the Herbert Power Stakes) and he didn't tumble into that this time," Hayes said.

"He rides a lot of trackwork for us and misses out on a lot of good Saturday rides, so it was a pleasure to give him the ride today.

"It's a great reward for all his hard work."

Parish was savouring the thrill of his first Group One win, five years to the day after making the move from New Zealand.

"First Group One and for it to be the Caulfield Cup - you beauty."